A light modulating material (hereinafter sometimes referred to as "light controlling material") comprising a liquid crystal and a supporting polymer shows an opaque state in the absence of an electric field ("off" state) because incident light is scattered therein due to a difference in refractive index between the polymer matrix and the liquid crystal, a spatial distortion of the liquid crystal director, discontinuity of the liquid crystal director among liquid crystal domains, and the like. In the presence of an electric field, the liquid crystal molecules are aligned in the direction of the electric field so that the refractive index of the liquid crystal becomes approximate to that of the polymer matrix to show a transparent state ("on" state). The "off" and "on" states occur reversibly.
Light modulating devices utilizing such optical properties are disclosed, e.g., in JP-A-64-62615 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and U.S. Pat. No. 4,435,047.
However, since the light modulating devices disclosed in the above publications usually assume white while in an opaque state, they are capable of controlling transmission of visible light to some extent but hardly capable of controlling transmission of longer wavelength light, especially near infrared to infrared light. Besides, the element disclosed in U.S. Pat. No. 4,435,047, which achieves displaying or light control by making use of changes of the liquid crystal state caused by a difference in temperature, is different from those utilizing application of an electrical field.
Near infrared to infrared light is heat rays and forms about 50% of sunlight. A light modulating device has been expected to control transmission of sunlight for making the atmosphere in the rooms and vehicles more comfortable. From this viewpoint, the above-described known light modulating devices fail to sufficiently serve for expected functions because of the poor control on near infrared to infrared light.
U.S. Pat. No. 4,707,080 discloses a light modulating device using a liquid crystal material containing two kinds of dichroic dyes, a black dye and a magenta dye. However, use of only two kinds of dichroic dyes as disclosed has a limit of capability in controlling color density, tone, and transmission of light inclusive of near infrared to infrared light.
On the other hand, when used as a display, etc., a light modulating device is required to exhibit appreciable light screening properties in the absence of an electric field and appreciable light transmitting properties in the presence of an electric field, that is, to make a high contrast between "off" and "on" states. Under the present situation, a sufficiently high contrast has not yet been achieved with any of the known light modulating devices, inclusive of the above-described elements containing two kinds of dichroic dyes as well as those containing no dichroic dye.
Further, it has been proposed to form an infrared light reflecting film made of, e.g., gold or Ti.sub.2 O/Ag/Ti.sub.2 O, on a light modulating device thereby to reduce infrared light energy as disclosed in U.S. Pat. No. 4,749,261 and JP-A-2-289782. This means being taken singly, it follows that the light modulating device always reflects infrared light, failing to control transmission of infrared light. If the infrared reflecting film is made thicker, transmission of light rays other than near infrared to infrared rays is also reduced, resulting in a reduction of total transmission. If the reflecting film is made thinner, on the other hand, the effect of infrared reflection would be lessened.